1. Field of the Invention
The present invention relates to an optical pickup apparatus, and more particularly, to a compact slim optical pickup apparatus which can adopt an existing laser diode and photo diode having a conventional size.
2. Description of the Related Art
Optical pickup apparatuses radiate light at optical discs to record information or generate electrical signals from light reflected from the optical discs to reproduce information. They are used in apparatuses such as audio or video optical disc players. Optical pickup apparatuses occupy relatively wide space within the apparatuses adopting them. Accordingly, to use the optical pickup apparatuses for light compact apparatuses such as portable or car, audio or video, optical disc players, it is necessary to decrease the volume and thickness of the optical pickup apparatuses.
Generally, the size of an optical pickup apparatus is determined according to the thickness and working distance of an objective lens, which determine an optical efficiency of recording information on and/or reproducing information from an optical disc. To realize a compact slim optical pickup apparatus, it is necessary to reduce the size of the objective lens and other optical parts used in the optical pickup apparatus. Accordingly, it is necessary to reduce the size of a light source and photodetector. However, there is a limitation in reducing the size of the light source and photodetector.
A light source needs a heat sink such as a radiator plate which cools heat generated from the light source. Such a heat sink is provided around the light source and makes it difficult to reduce the size of a light source part, which includes the light source and the heat sink, below a certain size.
To reduce the size of a photodetector, extra manufacturing cost is required, thereby increasing the price of the photodetector.
Recently, a light source and a photodetector have been combined into a single optical module. Since a light source having high optical power is required with development of high-speed and high-density optical pickup apparatuses, it is more difficult to reduce the size of the optical module.
To solve the above problems, for example, Korean Patent Publication No. 98-4432 proposed a slim optical pickup apparatus whose size is reduced by providing a refractor on an optical path to refract a horizontal beam downward in a light emission unit.
FIG. 1 shows the conventional slim optical pickup apparatus disclosed in the Korean Patent Publication No. 98-4432. The apparatus includes a light source 11 which emits a horizontal beam, a refractor 13 which refracts the beam incident from the light source 11 downward, a mirror 15 which reflects the beam incident from the refractor 13 upward, a focusing unit 17 which focuses the reflected beam on a recording surface of a recording medium 19, and a photodetector (not shown) which receives a beam reflected from the recording surface of the recording medium 19 through the optical path.
However, the above mentioned conventional slim optical pickup apparatus uses a hologram as the refractor 13. Accordingly, an optical efficiency may decrease. Moreover, since a beam is incident on the mirror 15 on a slant, the beam may be blocked by the focusing unit 17, that is, a holder supporting an objective lens. Reference numeral 12 denotes holders of the focusing unit 17, and reference numeral 18 denotes a base for the light source 11.
To overcome the above problems, for example, Korean Patent Publication No. 96-2205 proposed another slim optical pickup apparatus using beam shaping prisms 3a and 3b which are designed such that the diameter of an incident beam on an entrance surface is reduced and shaped, and an outgoing beam forms an angle of 45° with an outgoing surface and is perpendicular to the incident beam, as shown in FIG. 2.
FIG. 2 shows that the above slim optical pickup apparatus includes the beam shaping prisms 3a and 3b for an optical disc recording apparatus, a light source 1, a collimating lens 2, a mirror 5, an objective lens 6, a recording medium 7, an aberration compensating lens 8, a beam splitter 9, photodetectors 10 and a base 28 for the light source 1.
The beam shaping prisms 3a and 3b change the non-uniform distribution of intensities of incident beams in a vertical or horizontal direction to shape the incident beams into a particular shape (a circular shape), and make outgoing beams perpendicular to the axis of an initial incident beam, thereby realizing the vertical or horizontal structure of an optical pickup apparatus for an optical disc.
Accordingly, use of a pair of beam shaping prisms makes it possible to manufacture a compact optical pickup apparatus having a uniform light intensity distribution. However, the pair of beam shaping prisms may cause chromatic aberration depending on the temperature. Moreover, strict tolerance is required to assemble the beam shaping prisms.